Scheme 1. Role of UDP-diacylglucosamine pyrophosphatases in lipid A biosynthesis.
LpxH is primarily found in γ- and β-proteobacteria, whereas LpxI is present in α-proteobacteria, many δ-proteobacteria, and some environmental isolates, as described in detail in Supporting Table 2. Chlamydia and Cyanobacteria contain neither LpxH nor LpxI, but do possess LpxD and LpxB. Protein sequence data can be found at (http://www.ncbi.nlm.nih.gov/sutils/genom_tree.cgi).